Crohn's disease (CD) is a genetically complex disease in which both genetic susceptibility and environmental factors play key roles in the development of the disorder. NOD2/CARD15 mutations are associated with CD. NOD2 encodes for a protein that is an intracellular receptor for a bacterial product (muramyl dipeptide), though the exact functional consequences of these mutations remain the subject of debate. NOD2/CARD15 mutations are associated with ileal CD, with stricturing behavior, and possibly with a more complicated course of CD. NOD2/CARD15 mutations associated with CD have demonstrated heterogeneity across ethnicities and populations throughout the world, with regional variations across Europe and Spain. However, "NOD2/CARD15 testing" is not yet ready for use in the clinical setting. One of the reasons is that we know that these genetic variants increase the risk of disease only marginally, and many healthy individuals carry the risk alleles, at present it is not recommended to screen first-degree relatives, because we do not have the ability to prevent the disease at the present time.